Graphics Reference
In-Depth Information
Chapter 7
Volumetric Fluid, Smoke, and Fire
Oneofthemostimportant reasonstousesimulations in3Dworkistoobtain effects that wouldbeextremely dif-
ficult or impossible by using only traditional methods of mesh modeling and keyframe animation. Free-flowing
fluids and smoke are good examples of this. In this chapter I'll talk about Blender's powerful volumetric fluid
andsmokesimulationtools,whicharecapableofanimatingawidevarietyoffluidandsmokescenesmuchmore
realistically than could be done by hand.
In this chapter, you will learn to
• Use the Blender fluid simulator
• Get the shot
• Simulate smoke and fire
Using the Blender Fluid Simulator
Blender'sfluidsimulatorwasdevelopedasaprojectsponsoredbytheGoogleSummerofCode2005.Theofficial
name of the simulator is the El'Beem Fluid Simulator, a play on the name of the method it uses to calculate de-
formations, the Lattice-Boltzmann method.
The
Lattice-Boltzmann method (LBM)
is a state-of-the-art technique in computational fluid dynamics for cal-
culating the movement of fluid surfaces. It operates by treating the fluid surface as a lattice of triangles over
which alargenumber ofparticles travel andcollide with each other.The transference offorce fromthe collisions
of the particles drives the movement of the fluid surface. This method is capable of producing convincing fluid
movement and allowing a variety of parameter settings to influence the characteristics of the fluid. Furthermore,
itscalculationsarelocalandsothealgorithmcanbeparallelized.LBMisagoodmethodforsimulationsinwhich
detailedinteractionbetweenthefluidandsolidobjectsisdesirable,asinthecaseofCGanimation.LBMalsohas
thepotentialforconsiderablyexpandedfunctionalityinthefuture.Fornow,thereismorethanenoughinteresting
and useful functionality to keep Blender users busy exploring the potential of fluid simulation, so let's get to it.
Getting Started with Fluids
Everyfluidsimulationhastwonecessarycomponents.Thefirstisadefinedareainwhichtocarryoutthesimula-
tion, and the second is a source for the fluid itself. The fluid simulation algorithm operates by dividing space into
discrete units called
voxels
. You can think of voxels as being something like 3D pixels. In fact, the word
voxels
derives from the words
volumetric
and
elements
, just as
pixels
derives from
picture
and
elements
. In the same
way that a single image or display must be limited to a finite number of pixels, an area of calculation for fluids
is limited to a portion of space that can be divided into a finite number of voxels. This portion of space is called
